Optical Path - Practice Questions & MCQ

Optical path-

It is defined as the distance travelled by light in a vacuum, in the same time in which it travels a
given path length in a medium.

Let light cover distance t in the medium having a refractive index as  in Time T.

So   where v=speed of light in the medium

and   where c=speed of light in the vacuum.

So 

So in the same time T distance covered by light in a vacuum is 

So the relation between geometrical path (t) and optical path (l) is given as 

• For two medium in contact as shown in the below figure

the optical path is equal to 

• Change in the optical path in a transparent slab

Consider the following two cases

Case I-  A light cover distance 

So the optical path in this case is 

Case II- Now a slab of thickness t is placed between A and B

So distance travells in slab=t

and distance travells in air=

So the optical path in this case is  

Now change in the optical path = 

I.e due to insertion of the slab the optical path is increased by